1. Field of the Invention
This invention relates generally to oscillators, and more specifically, to an accurate resistor-capacitor (RC) oscillator having a frequency which is power supply voltage independent and a method therefor.
2. Background of the Invention
Oscillator circuits are used in a myriad of applications in the electronics industry for providing clock and other timing signals to electronic circuitry such as microprocessors, microcontrollers, flip-flop circuits, latch circuits, charge pumps, etc. A common type of oscillator circuit is the resistor-capacitor (RC) circuit. An RC oscillator circuit typically includes a control circuit which is coupled to the RC network. The control circuit is used for alternatively charging and discharging the capacitor through the resistor to generate an oscillatory signal. The frequency of oscillation is determined by the time constant of the resistor and capacitor.
Even though the frequency of oscillation is primarily dependent on the RC network, the frequency is also affected by the power supply voltage. The control circuitry of the RC oscillator is typically comprised of a plurality of CMOS transistors. A fundamental function of CMOS circuitry is that as power supply voltage is lowered, activity slows down. Thus, in an RC oscillator having CMOS transistors, the frequency of oscillation will tend to slow down as the power supply voltage is lowered.
Therefore, a need existed to provide an improved oscillator circuit and a method therefor. The improved oscillator circuit and a method therefor must be more accurate than prior art RC oscillator circuits. The improved oscillator circuit and method therefor must also be able to generate a frequency of oscillation which is independent of the power supply voltage.